Abstract
BackgroundThe longer upper airway is more collapsible during sleep. This study aims to reveal relationships among upper airway length, weight, and obstructive sleep apnea (OSA), particularly to answer why the upper airway of OSA patients is longer than that of healthy people and why some obese people suffer from OSA while others do not.MethodsWe perform head and neck MRI on male patients and controls, and measure > 20 morphological parameters, including several never before investigated, to quantify the effect of weight change on upper airway length.ResultsThe upper airway length is longer in patients and correlates strongly to body weight. Weight increase leads to significant fat infiltration in the tongue, causing the hyoid to move downward and lengthen the airway in patients. The apnea-hypopnea index (AHI) strongly correlates to airway length and tongue size. Surprisingly, a distance parameter h and angle β near the occipital bone both show significant differences between healthy males and patients due to their different head backward tilt angle, and strongly correlates with AHI. The contributions of downward hyoid movement and head tilt on airway lengthening are 67.4–80.5% and19.5–32.6%, respectively, in patients. The parapharyngeal fat pad also correlates strongly with AHI.ConclusionsThe findings in this study reveal that the amount of body weight and distribution of deposited fat both affect airway length, and therefore OSA. Fat distribution plays a larger impact than the amount of weight, and is a better predictor of who among obese people are more prone to OSA.
Highlights
Obstructive sleep apnea (OSA) is characterized by repeated collapse and obstruction of the upper airway (UA) during sleep [1]
We will test the hypothesis: both the amount of body weight and distributions of deposited fat in the head and neck can affect airway length, but the fat distribution dominates the change in UA length and determines who among obese people are more prone to obstructive sleep apnea (OSA)
In addition to confirming that UA of OSA patients is much longer than in healthy subjects, and that Length of the upper airway (LUA) is positively correlated with apnea-hypopnea index (AHI) as observed in some studies [8], we find the significant impact of body weight on LUA and the mechanism of UA lengthening in obese people, suggesting that weight gain increases LUA and the risk of UA collapse during sleep
Summary
Obstructive sleep apnea (OSA) is characterized by repeated collapse and obstruction of the upper airway (UA) during sleep [1]. Previous studies have revealed that a longer airway has a considerably less negative closing pressure and is more collapsible [4]. Studies show a correlation between UA length and OSA severity [7, 8]. The mechanism of UA lengthening in OSA patients is unclear. The longer upper airway is more collapsible during sleep. This study aims to reveal relationships among upper airway length, weight, and obstructive sleep apnea (OSA), to answer why the upper airway of OSA patients is longer than that of healthy people and why some obese people suffer from OSA while others do not
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